Extracellular invertase: key metabolic enzyme and PR protein

Abstract

Extracellular invertase is the key enzyme of an apoplasmic phloem unloading pathway and catalyses the hydrolytic cleavage of the transport sugar sucrose released into the apoplast. This mechanism contributes to long-distance assimilate transport, provides the substrate to sustain heterotrophic growth and generates metabolic signals known to effect various processes of primary metabolism and defence responses. The essential function of extracellular invertase for supplying carbohydrates to sink organs was demonstrated by the finding that antisense repression of an anther-specific isoenzyme provides an efficient method for metabolic engineering of male sterility. The regulation of extracellular invertase by all classes of phytohormones indicates an essential link between the molecular mechanism of phytohormone action and primary metabolism. The up-regulation of extracellular invertase appears to be a common response to various biotic and abiotic stress-related stimuli such as pathogen infection and salt stress, in addition to specific stress-related reactions. Based on the observed co-ordinated regulation of source/sink relations and defence responses by sugars and stress-related stimuli, the identified activation of distinct subsets of MAP kinases provides a mechanism for signal integration and distribution within such complex networks. Sucrose derivatives not synthesized by higher plants, such as turanose, were shown to elicit responses distinctly different from metabolizable sugars and are rather perceived as stress-related stimuli.

Regulation of Arbuscular Mycorrhization by Carbon. The Symbiotic Interaction Cannot Be Improved by Increased Carbon Availability Accomplished by Root-Specifically Enhanced Invertase Activity

“…A strong induction of extracellular invertases in plants and the severe modulation of source-sink activities could also lead to an activation of defenserelated mechanisms via sugar-mediated gene expression (Rolland et al, 2002;Roitsch et al, 2003). As shown previously, constitutive expression of the apoplast-located yeast invertase resulted in a strong accumulation of PR protein transcripts in tobacco leaves, encoded by PAR1, PR-1b, and PR-Q (Herbers et al, 1996).…”

“…If the fungus is able to take up hexoses via intraradical hyphae, as shown for isolated hyphae (Solaiman and Saito, 1997), the number of arbuscules might decrease, indicating that the fungus does not fulfill its part in the symbiosis any longer. Another possibility might include activation of defenserelated mechanisms in the plant root via hexose sensing (Herbers et al, 1996;Rolland et al, 2002;Roitsch et al, 2003), which can interfere with the mutualistic interaction, resulting in diminished mycorrhization.To study the impact of altered hexose availability on mycorrhization of tobacco or M. truncatula two general approaches were followed. To increase root hexose content, yeast (Saccharomyces cerevisiae)-derived invertase(s) were expressed either under control of a chemically inducible promoter in tobacco or in hairy roots of M. truncatula following Agrobacterium rhizogenes transformation.…”

“…If the fungus is able to take up hexoses via intraradical hyphae, as shown for isolated hyphae (Solaiman and Saito, 1997), the number of arbuscules might decrease, indicating that the fungus does not fulfill its part in the symbiosis any longer. Another possibility might include activation of defenserelated mechanisms in the plant root via hexose sensing (Herbers et al, 1996;Rolland et al, 2002;Roitsch et al, 2003), which can interfere with the mutualistic interaction, resulting in diminished mycorrhization.…”

Sugar metabolism ofVetiveria zizanioidescells cultured with Amberlite XAD-4. Uptake of radiolabelled sugars, cell wall invertase activity and gene expression

“…In the case of cultured tissues, however, invertases may be secreted into the medium also (Shin et al 2003) and a novel isoform of acid invertase, which is not bound to the cell wall, has been characterized (Kim et al 2000). Depending on the species and cell type, hexoses released into the culture media are then taken up by passive or active processes, through hexose-specific transporters (Stepan-Sarkissian and Fowler 1986;Roitsch et al 2003;Kato et al 2007). Once inside, hexoses have a great capacity to stimulate specific sugar sensors (Koch 2004 and references therein) and the resulting signals can alter expression of diverse genes (Smeekens 2000;Rolland et al 2002;Sherson et al 2003).…”

Influência da poda de renovação e controle da ferrugem nas reservas de carboidratos e produção de pessegueiro precoce

“…Nas plantas de modo geral, durante o crescimento vegetativo, a maioria dos carboidratos é transportada para as raízes e folhas jovens, enquanto, após o florescimento, os carboidratos são direcionados prioritariamente para os frutos, tubérculos e raízes de reservas (Roitsch et al, 2003).…”